Link Bonding

Aggregating two or more links to achieve one fat link brings a number of advantages, in short more bandwidth. We already had such a technology in place on the local network known as IEEE 802.1AX link aggregation, or Ethernet bonding. Now products exist, which make this capable over the internet and over layer 3 of the OSI layer.

With Link Bonding on the WAN side you would need two appliances on each end. If it’s VPN bonding the two appliances would be configured on each site to bond the many internet connections together to act as one fat link, though giving IPSec VPN more bandwidth.

If its WAN bonding that is required for general traffic, an appliance would sit in the organisations site and another appliance at the ISP end. At the company site they could then bond the many links to the fat pipe at the ISP end to create this one big virtual connection. Of course if there’s two or more internet links which would have their own public IP addresses, when bonded together the many links would be acting as one link. Therefore there’s the need for a bonded singlevirtual IP address which is assigned by the ISP.

Link Bonding vs Link Balancing

For resilience, more bandwidth and throughput, organisations invest in a 2nd 3rd 4th or more internet connections.

If any of the Internet connections go down, these will failover to the other connections. The remaining Internet connections will just take on the entire load.

The load on these connections are balanced using some sort of balancing protocol, such as round robin, least weight, etc. So the first connection will go down the 1st link, 2nd connection down 2nd and so on if we were to use round robin. Also for example you can define other criteria such as using one connection for VPN, another for SMTP and the last for browsing the web, and there are also many other ways balancing the load between the many connections.

This is great because an organisation can have two or more internet connections sharing the load, and if one goes down the other connection just takes all the remaining load. When the failed connection is back up, the load is balanced again on all connections. This is where the term load balancing comes from. The bandwidth, or connections are balanced between the number of internet connections.

However in some circumstances we need something more than just load balancing. For example if a user wanted to download a large file. This file will be downloaded from one of the available ISP links/connections. However what if all links were free to use at that particular time. Imagine if we could just aggregate the bandwidth of all links. How much quicker this large file would then take to download !

Fortunately we can do this using link bonding technology.

All links act as one big virtual link, which will allow this large file to download much faster when using link bonding.

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